d3/docs/d3-selection/events.md

Handling events

For interaction, selections allow listening for and dispatching of events.

selection.on(typenames, listener, options)

Source · Adds or removes a listener to each selected element for the specified event typenames.

d3.selectAll("p").on("click", (event) => console.log(event))

The typenames is a string event type, such as click, mouseover, or submit; any DOM event type supported by your browser may be used. The type may be optionally followed by a period (.) and a name; the optional name allows multiple callbacks to be registered to receive events of the same type, such as click.foo and click.bar. To specify multiple typenames, separate typenames with spaces, such as input change or click.foo click.bar.

When a specified event is dispatched on a selected element, the specified listener will be evaluated for the element, being passed the current event (event) and the current datum (d), with this as the current DOM element (event.currentTarget). Listeners always see the latest datum for their element. Note: while you can use event.pageX and event.pageY directly, it is often convenient to transform the event position to the local coordinate system of the element that received the event using d3.pointer.

If an event listener was previously registered for the same typename on a selected element, the old listener is removed before the new listener is added. To remove a listener, pass null as the listener. To remove all listeners for a given name, pass null as the listener and .foo as the typename, where foo is the name; to remove all listeners with no name, specify . as the typename.

An optional options object may specify characteristics about the event listener, such as whether it is capturing or passive; see element.addEventListener.

If a listener is not specified, returns the currently-assigned listener for the specified event typename on the first (non-null) selected element, if any. If multiple typenames are specified, the first matching listener is returned.

selection.dispatch(type, parameters)

Source · Dispatches a custom event of the specified type to each selected element, in order.

d3.select("p").dispatch("click")

An optional parameters object may be specified to set additional properties of the event. It may contain the following fields:

• bubbles - if true, the event is dispatched to ancestors in reverse tree order.
• cancelable - if true, event.preventDefault is allowed.
• detail - any custom data associated with the event.

If parameters is a function, it is evaluated for each selected element, in order, being passed the current datum (d), the current index (i), and the current group (nodes), with this as the current DOM element (nodes[i]). It must return the parameters for the current element.

pointer(event, target)

Source · Returns a two-element array of numbers [x, y] representing the coordinates of the specified event relative to the specified target.

const [x, y] = d3.pointer(event);

event can be a MouseEvent, a PointerEvent, a Touch, or a custom event holding a UIEvent as event.sourceEvent.

If target is not specified, it defaults to the source event’s currentTarget property, if available. If the target is an SVG element, the event’s coordinates are transformed using the inverse of the screen coordinate transformation matrix. If the target is an HTML element, the event’s coordinates are translated relative to the top-left corner of the target’s bounding client rectangle. (As such, the coordinate system can only be translated relative to the client coordinates. See also GeometryUtils.) Otherwise, [event.pageX, event.pageY] is returned.

pointers(event, target)

Source · Returns an array [[x0, y0], [x1, y1]…] of coordinates of the specified event’s pointer locations relative to the specified target.

const points = d3.pointers(event);

For touch events, the returned array of positions corresponds to the event.touches array; for other events, returns a single-element array.

If target is not specified, it defaults to the source event’s currentTarget property, if any.